Self-inking material



July 18, 1967 Filed April 15. 1963 SYNTHETIC RUBBER WATER 2 CC vomsszumuvozoxlof o5 Gra/ams I-O GRAMS wwe oxwf Fez oa MAGNESIUM CARBONATE wanensucnosf GLYCERlN reame oxme Fezog KIESELGUHR METHYL vloLET GLYCERLNE zmcSTE MATE suLPuua l meseLsus-urz y I6 :mc summe l I mw-nv f I I4 f/lulalll/1,

MOULD QURFACES I3 PAINT ALL JTIG l MouLD #.cuas 300F Remove mom MOULD F.A. DEUTER SELF-INKING MATERIAL 3 Sheets-Sheet l 15 Gams E Mlx IGRAMMASTICATE 8 GRAMS G C.C. l GRAMQ MASTICATE 4 GRAMS MASTICHTE 4 eAMs ROLLJuly 18, 1967 F; A. DEUTER 3,331,794

l SELF-INKING MATERIAL Filed April 1e, 196s s sneets-sneet 2 WATER IS CC.

POTASSIUM HYDROKIDE 0-5 GQAMS FERRIC OXIDE Fez O3 l-O GRRMS MAGNESIUMCARBONATE 0-5GRAMS i MIX lo MAsncATE GLYCERINE SCC.

suena o-5G2AMs summe s @RAMs MESELGUHR 's GRAMs i I Y Y l0 srEAmc Aclo nPmzrs SYNTHETIC RUBBER 20 GRAMS GLYCERINE. 6B PARTS WARM X( STIR |07.Amm-mm Y sPARTs COOL METHYL VIOLT ZINC STEARATE KIESELGUHR I I l0MASTICATE SULPHUR GGRAMS ,o UREA SGRAMS MASTCA-[E WATER g QC I Mlx IMANEsmM cmzonmf mRAM July 18, 1967 Filed April 16, 196s SYNTHETIC RussiaNATURAL 'Rualz WATER poTAsssuM HYDRoxlof famme oxws Fezog GLYCEROL SUGARPERM: oxloe Pelo@ GAAPmTE KIE SELGUHR GLYCEROL WATER URBA AMMONIUMCARBONATE COOL 86.0. METHYL VIOLET mammals-* f- GRIND Q Mix i" STEARlCACID l'l GQAMS GLYCEROL so QQ lol AMMONIA SOLUTION WATER zlNc sTEARATE VSULPHUR ACCELERATOR F. A. DEUTER 3,331,794

SELF-INKING MATERIAL 5 Sheets-Sheet 3 17 GRAMS 3 GRAMS O l C.C.

O-S GRRMS l' 5 SRAM GRIN A M1 L '0 scc. MAsTicATE GRRMS i IO GAN A MIX l30 GRAMS O-Q GRAMS l HEATS. Msx j l MIX 2 HEAT COOL GGRANS o-2 GRAMS cGRAMs l l GQAM l l IO GRIND K Mlx 1f@ MAsTlcATE United States Patent O3,331,794 SELF-INKING MATERIAL Frederich A. Deuter, Hilton, SouthAustralia, Australia,

assigner of one-half to .lohn Foundas, South Australia, Australia FiledApr. 16, 1963, Ser. No. 273,462 Claims priority, application Australia,Apr. 19, 1962,

16,825/62; sept. is, 1962, 22,2s2/62 12 Claims. (Cl. 26d- 5) Thisinvention relates to a material of the type used for date stamps,registering iinger prints, and other similar purposes, which is arrangedto contain a certain quantity of dye so that the need for an inking padis eliminated.

One of the problems with rubber stamps of the type which are usedgenerally is lthe need for the use of a stamp pad to impart a iilm ofink to the surface of the rubber stamp before the rubber stamp isapplied -to the paper. Use of such a stamp pad is inconvenient in thatit needs to be purchased and retain, and secondly, that it slows up thestamping operation in the instance oi a number of similar impressionsbeing required to be applied in a short period of time. Quite clearlythe design of machines which utilise -rubber stamps and the like can beVery much simpliiied if the rubber stamps contain their own ink.

A further object of this invention is to provide a selfinking -materialwhich will tend to remain moist so as to impart an impression even underhot, dry conditions, but which will not tend to ood under moist, humidconditions.

In its simplest form this invention may be said to consist of asel-inlsing `material which com-prises rubber, a dye dispersedthroughout the rubber, hygroscopic substances dispersed throughout therubber, -a iiller dispersed throughout the rubber, and a Irelease agentdispersed throughout the rubber.

It will be seen that this invention makes possible -a selfinkingmaterial which is mechanically tough and will hold a large quantity ofdye, -so that lthe sel-inking material may be used for an extendedperiod of time without the need for replacement.

It will also be seen from this specification that this inventionprovides a means whereby a self-inking material which is extremelystable both lbefore and after vulcanising can be produced, and which iseasy to use in -a standard vuloanising set utilising resin based mouldsas commonly used in the rubber stamp industry.

It will be obvious to a skilled chemist that various types of rubber canbe used `in this invention, that the methyl violet dye describedhereunder can be replaced with other dyes, that a wide variety ofhygroscopic substances are available for selection which are suitablefor dispersal throughout rubber, and that various llers and releaseagents can be used. However, for the invention to be more clearlyunderstood, it is described hereunder in some detail with `reference tothree separate embodiments with Ireference to and illustrated in theaccompanying drawings in which:

FIG. 1 is Ia diagrammatic representation of a first embodimentindicating the steps of producing a rubber stamp pad,

FIG. 2 is a diagrammatic representation showing the steps of producingself-inking material according to a second embodiment, and

FG. 3 is a diagrammatic representation of lthe steps for producing aself-ink-ing material Iaccording to -a third embodiment.

Referring to the first embodiment, quantities indicated are suitable forlaboratory purposes, but it will be appre- BJM Patented July 18, 1967lCe ciated that they can be increased proportionally for commercialproduction and also varied to meet the d-iiferent requirements due toclima-tic conditions, rate of usage of ink and the like.

In this rst embodiment which is illustrated in FIG. 1, 15 `grams ofsynthetic isopren-e rubber is Imixed with 2 ce. of water, 0.5 gram ofpotassium hydroxide and 1.0 gram of ferrie oxide (Fe203). The waterfunctions as' a solvent for the potassium hydroxide and is absorbed intothe rubber itself by mastication which is assisted by the ferrie oxide,the potassium hydroxide functions as a catalyst to c-atalyse theglycerine which is added later to for-m complex resins, while the ferricoxide is hygroscopic, assists penetration of the potassium hydroxidesolution, and toughens the rubber to stand penetration of glycerinewhich otherwise 4breaks down rubber.

The materials are masticated in a masticator l0 for a period of time,after which l gram of magnesium carbonate (levis), 3 cc. of water l gramof sucrose, 4 cc. of glycerine, 1 gra-m of ferrie oxide and 4 grams ofkiesel'gulhr are added while mastication continues. The function of theferrie oxide and magnesium carbonate is to assist mastication. Theglycerine and sucrose form an extremely hygroscopic mix, the sucroseincreases the hygroscopic eiiect and assists in lfreeing of ink which issubsequently added, the glycerine is hygroscopic, carries moisture intothe rubber, and provides an ink-retaining medium, While the kieselguhrfunctions as a ller to form body, and absorbs the glycerine and methylviolet subsequently added to form a mixture capable of retaining the inkcontent and releasing it on the presence of moisture. If desired alittle gelatin may also be used here, but it is found that gela-tinecauses swelling in the rubber after it is vulcanised, and therefore theuse of gelatine does not form -pa'rt of thi-s embodiment.

'il-he mastication is again continued for a period of time, after which8 grams of methyl violet, 6 cc. of glycerine and 1 gram of zinc stearateare added. The zinc stearate has the effect of assisting mastication ofthe additional -glycerine with the methyl violet, prevents tackinesswith respect to lrollers Vand the rolling of the material, and assistsin releasing the rubber mixture when moulded. T'he methyl violet, ofcourse, functions to provide the ink for the mixture and also acts as anaccelerator. It is noted that the complete mixture is self-curing toquite an extent yclue to the presence of the methyl violet, when theiinal product is exposed to air.

Mastication is further continued, and 4 grams of sulphur are then added,and mastication is further continued for a period of time. A stillfurther 4 grams of kieselguhr is then masticated in to -absorb anysurplus moisture and glycerine, and thus render the mixture (which isplasticised by this stage) easier to handle.

The mixture is then fed through rollers 11 which callender theplasticised mass, and portion of the mixture is placed into a mould 12.The mould 12 consists of a base plate 13 of mild steel, a plastic basedmould plate 14 which is used in accordance with the ordinary practice ofmoulding rubber stamps, a marginal plate 15 which surrounds theplasticised mass wtihin the mould 12, and a top plate 16. All theseplates are themselves coated with the zinc steal-ate which functions asa release agent. The rubber is moulded under pressure for a period offrom four to ve minutes at a temperature of 300 Fahrenheit. By usingmild steel plates and zinc stearato, it is found that the mouldedarticle is readily released from the mould and retains sharpcharacteristics which are a true complementary representation of theconfiguration of the face of the mould. It will be seen that thethickness of the plate 15 governs the thickness of the linal productwhen removed from the mould, and it is found in prac- 'Y tice that thisthickness for a rubber stamp needs to be about 3 millimeters. Y

It is found that the completed stamp after moulding should be left for aperiod of from three to ve days before being used, after which it willcontinue to re-ink itself without the need to apply it to anink-containing pad.

Color changes in the inking can be made if desired by utilising dyesother than methyl violet.

According to a further embodiment which is illust-.rated in FIG. 2, amixture of ammonium stearate and glycerine is first made as follows:

17 parts by weight of stearic acid (commercial) Yare warmed until meltedand then have added to them 88 parts by weight of glycerine, and themixture is vigorously stirred.

3 parts of dilute ammonia (10%) are then mixed with 12 parts ofdistilled water, and this is mixed in with the glycerine Iand stearicacid while continuingV to stir and keeping the temperature so that thestearic acid remains melted until the ammonia is added. The heat is thenremoved but the product is kept stirred until eventually a paste isformed. In this embodiment the commercial stearic laciclused containedonly about 45% of pure stearic acid, with about of oleic and 50% ofpalrnitic acids.

Five'separate mixtures were then made as follows:

Mixture No. 1.-Into 1.5 cc. of water, 0.5 gram of .potassium hydroxide(KOH) was thoroughly dissolved,

1 gram of ferric oxide (Fe203) and l0.5 gram of magnesium carbonate(MgCO3) (levis) were added.

Mixture No. .2.-5 cc. of glycerine and 0.54 gram of sugar werethoroughly mixed, and 1.5 grams of graphite and 3 grams of kieselguhrwere added and mixed.

Mixture No. .3.- grams of the paste containing ammonia with glycerineand stearic acid was mixed with 6 gramsV of methyl violet, and thenmixed with 1 gram of zinc stearate and 2 grams of kieselguhr.

-Mz'xture No. 4.-Mixture No. 4,cons1sts solely of 6Y grams of sulphur.

Mixture No. 5.-3 grams of urea crystals were thoroughly dissolved in 3cc. of water, 1 gram of magnesium carbonate (MgCOg) (levis) was Iaddedand 2 gramsof kieselguhr were then added.

The mixtures were then milled with synthetic rubber (syntheticpolyisoprene) as follows:

20 grams of synthetic polyisoprene were masticated with the mixturesbeing added in the order specified above, No. l first and in sequenceuntil No. 5 last.

'It has been found that the amount of synthetic polyisoprene may bevaried to give variable inking strengths to Vthe rubber mixture, andafter milling, the rubber mixture can be vulcanised -at 300 F. for 4minutes keeping it enclosed as described above.

The above two embodiments have been found to produce self-inkingmaterial which is very satisfactory in general use, but certainimprovements have been found by utilising the third embodiment which kisdescribed hereunder with reference to FIG. 3. Among these improvementshas been a toughening of the rubber, a more rapid re-inking, so that thematerial can be used for a rubber stamp to apply impressions in quicksuccession, y

and less tendency to dood In this third embodiment grams of syntheticrubber` (synthetic polyisoprene) are mixed with 3 grams of naturalrubber and these two ingredientsrare thoroughly masticated in themasticator 10.

Three mixtures are prepared in theffollowing proportions: Y

Mixture (a).-Water H2O 1 cc., potassium hydroxide KOH 0.5 gram, fern'coxide Fe203 1.5 grams.

Mixture (b).-17 grams of stearic Vacid are gently Vheated until meltedand then mixed with 70 cc. of glycerol,

keeping the mixture in a melted state. 3 cc. of 10% aqueous ammoniasolution are then mixed in with 12 cc. of water and this in turn isAmixed in with the stearic acid and glycerol mixture until the massbecomes homogeneous. The mass is then'allowed Yto cool whereupon themixture forms `a thick paste.

Mixture (c).-1 8 cc. of glycerol, 21 cc. of water, 30 grams of urea, and0.6 gram of ammonium carbonate are mixed together, and the mixture isgently heated until all salts are in solution.

The mixture (a) is then added to the masticated rubber mixture.

A further mixture is then Vmade between 3 cc. of glycerol, 0.5 gram ofsugar, 0.5 gram of ferrie oxide, 1.5 grams of graphite and 3 grams ofkieselguhr, and after this has been thoroughly mixed it is masticated inwith the rubber'together with the mixture (a) in the masticator 10.

8 cc. of mixture (c) are then mixed with 10 grams of methyl violet, 6grams of mixture (b) 0.2 grams of zinc stearate, 6 grams of sulphur andl gram of accelerator (Vulkacit P (piperidinium pentamethylene dithiocarbamate) as manufactured by Farbenfabriken Bayer A/ G, Leverkusen,Germany).

The above are all mixed together in the order specified, and whencompletely mixed together are added to the mixture being masticated. Y Y

The potassium hydroxide appears to act as a catalyst forming variouscomplex resins of the glycerol.

The ferric oxide is hygroscopic and appears to toughen the rubbermixture. It also acts as a dispersal agent for the potassium hydroxide.

of the rubber and in the absorption of the dye in an available form.

The urea mixture is very hygroscopic and also assists w in theabsorption of the dye in an available form.

The glycerol mixture with graphite, sugar, ferrie oxide and kieselguhrserves to prepare the rubber for the Y masticating and dispersal of thedye mixture, and also to assist the dye absorption. The graphite servesto toughen the rubber when it is vulcanised and also prevents the rubberfrom getting tacky after it has been vulcanised. It also keeps workingwithin the rubber as it is used in the form of a stamp and tends toimprove the inking of the rubber when so used.

The kieselguhr acts to assist the mastication and also functions as afiller.

The zinc stearate improves the ink mixture and also assists in thepreventing ofthe rubber. from getting tacky. It further assistsvulcanisation to some extent.

The sulphur is of courser for the purpose of vulcanisation j and alsoappears to assist in rendering the dye mixture available on contact withmoisture from the atmosphere, together with the urea mixture.

It is not necessary to adhere strictly t-o the proportions stated inthis embodiment to obtain a self-inking rubber material, and othermaterials may be used ifdesired. For example magnesium carbonate,sodiumlactate (which is very hygroscopic), gelatin (in small quantitiesonly), and sodium stearate, but it will be found that the substances inthe proportion stated in this third embodiment appear to give very goodself-inking rubber material.

The material may be vulcanised atabout 300'degr`ees Y F. inapproximately five minutesY if kept sealed from contact with the air.

In air the rubber is self-curing to some extent but a much bettermoulding is produced when the rubber is vulcanised out of contact withthe air and under pressure. This can be achieved as in the firstembodiment.

It Vmight Vbe noted that in general it is desirable toY maintainV thetemperature of the masticatingrollers at about F. Thus for example inthe third embodiment i to room temperature before adding the finalsubstance which includes the methyl violet.

Different colors may be obtained by using -different dyes in place ofthe methyl violet without otherwise altering the procedure in any otherway. The following are typical examples:

Red can be obtained by usin-g magenta dye.

Blue can be obtained by using methylene blue dye.

Results have also been obtained by using bronze scarlet for red andAstra blue for blue, and nigrosine black. Nigrosine black however wasinferior to the other dyes mentioned.

The formulas for the first three dyes and the accelerator mentioned areas follows:

Methyl Volet.-Methylrosaniline chloride.

Magenta.-(Fuchsin) a mixture lof rosaniline and pararosanilinehydrochlorides.

M ethylene Blue.-Methylthionine chloride Accelerator-. Piperidiniumpentamethylene dithiocarbamate.

It is found that the mixture referred to as mixture (b) in the thirdembodiment is suitable as a release agent for application to the dyesand moulds before moulding, but it is preferred that the release agentshould be without urea.

It is found that the rubber as mixed before vulcanising is extremelyhydroscopic and it is therefore desirable that it should be kept fromcontact with the air, for example by storing in polyethylene bags.

What I claim is:

1. A self-inking material comprising rubber selected from the groupconsisting of natural rubber, synthetic polyisoprene, and a mixture ofnatural rubber and synthetic polyisoprene, said rubber containing:

(I) the following materials dispersed throughout the rubber, an organicdye; hygroscopic substances including glycerol present in sufficientamount to retain moisture and provide an ink-retaining medium; discretefiller materials inert with respect to said rubber, and a release agentpresent in sucient amount to prevent tackiness of the material,comprising a fatty acid material or salt thereof dispersed throughoutthe rubber, and

(II) potassium hydroxide in said rubber present in sufficient amount tocatalyze formation of dye retention resin molecules within the rubber,the dye retention resin molecules releasing dye upon absorption ofatmospheric moisture into the rubber by the hygroscopic substances.

2. A self-inking material comprising rubber selected from the groupconsisting of natural rubber, synthetic polyisoprene, and a mixture ofnatural rubber and synthetic polyisoprene, said rubber containing (I)the following materials dispersed throughout the rubber, -an organicdye; hygroscopic substances, including glycerol, present in sufficientamount to retain moisture and provide an ink-retaining medium; discretefiller materials inert with respect to said rubber, and a release agentpresent in sufiicient amount to prevent tackiness of the materialcomprising a fatty 'acid material or salt thereof dispersed throughoutthe rub-ber, and

(il) potassium hydroxide within the rubber present in sufficient amountto catalyze reaction of the rubber and glycerol to form dye retentionresin molecules thereby rendering the rubber dye retaining, the dyeretention resin molecules releasing dye upon absorption of atmosphericmoisture into the rubber by the hygroscopic substances.

3. -A self-inking material comprising rubber selected from the groupconsisting of natural rubber, synthetic polyisoprene, and a mixture ofnatural rubber and synthetic polyisoprene, said rubber containing lo insufficient amount to catalyze reaction of the rubber and glycerol toform dye retention resin molecules thereby rendering the rubber dyeretaining, the dye retention resin molecules releasing dye uponabsorption of atmospheric moisture into the rubber by the hygroscopicsubstances.

4. A self-inking material comprising synthetic polyisoprene, an anilinedye; hygroscopic substances present in sufficient amount to retainmoisture and provide an ink-retaining medium including ferrie oxide,glycerol, sucrose and urea; filler materials including kieselguhr andgraphite; a release agent present in sufiicient amount to preventtackiness of the material including zinc stearate; sulphur present insufiicient amount to allow vulcanization, dispersed throughout theisoprene, and potassium hydroxide present in sufficient amount tocatalyze formation of dye retention resin molecules within the syntheticpolyisoprene.

5. A self-inking material comprising synthetic polyisoprene, an anilinedye; hygroscopic substances present in sufficient amount to retainmoisture and provide an ink-retaining medium including ferrie oxide,glycerol, sucrose and urea; filler materials including kieselguhr andgraphite; a release agent present in sufficient amount to preventtackiness of the material including zinc stearate and stearic acid;sulphur present in sufdcient amount to allow vulcanization; anaccelerator dispersed throughout the synthetic polyisoprene, andpotassium hydroxide present in sufiicient amount to catalyze formationof dye retention resin molecules within the synthetic polyisoprene,

6. A self-inking material comprising rubber consisting of a mixture ofnatural rubber and synthetic polyisoprene,

a rst homogeneous mixture containing potassium hydroxide present insufficient amount to catalyze formation of dye retention resin moleculeswithin the rubber and a hygroscopic substance present in suiiicientamount to retain moisture and provide au inkretaining medium,

a second homogeneous mixture containing glycerol, 5 ferrie oxide, andfiller material,

a third homogeneous mixture comprising a first sub-mix which itselfcomprises glycerol and urea; a second sub-mix which comprises the firstsaid sub-mix together with an analine dye; a third sub-mix which itselfcomprises stearic acid and an aqueous ammonia solution; and zincstearate, sulphur present in sufiicient amount to allow vulcanizationand an accelerator, all said homogeneous mixtures being dispersedthroughout the rubber.

60 7. A self-inking material comprising rubber consisting of a mixtureof natural rubber and synthetic polyisoprene,

a first homogeneous mixture containing water, potassium hydroxidepresent in sufiicient amount to catalyze formation of dye retentionresin molecules within said mixture, and ferrie oxide,

a second homogeneous mixture containing glycerol, su-

crose, ferric oxide, graphite and kieselguhr, and

a third homogeneous mixture comprising a first sub- -mix which itselfcontains glycerol, water, urea and ammonium carbonate;

a second sub-mix which contains the said first sub-mix together withmethyl violet;

a third sub-mix which itself contains stearic acid,

glycerol, aqueous ammonia solution and water; and zinc stearate, sulphurpresent in suicient amount to of a mixture of natural rubber andsynthetic polyisoprene,

a rst homogeneous mixture containing 1 part by Weight of water, 1/2 partby weight of potassium hydroxide and 11/2 parts by Weight of ferrieoxide,

a second homogeneous mixture containing 3-1/2 parts by the rubber.

9. A self-inking material comprising rubber consisting a mixture ofnatural rubber and synthetic polyisoprene,

a rst homogeneous mixture containing 1 part by 8 geneity zinc stearate,sulphur, accelerator, said second sub-mix and said third sub-mix, andmasticating the third homogeneous mixture into the rubber. 11. Themethod of `preparing the self-inking material of 5 claim 3 comprisingthe steps: f

masticating together synthetic polyisoprene and natural rubber,

grinding and mixing to homogeneity a mixture containing potassiumhydroxide and ferrie oxide, and after Weight of glycerol, 11/2 parts -byweight of graphite l0 mixing, masticating same into the rubber at atemand 3 parts by Weight of kieselguhr, and perature of about 90 F.,

a third homogeneous mixture comprising 8 parts by grinding and mixing tohomogeneity a mixture con- Weight of a -irst sub-mix which itselfcontains 22 taining glycerol, sucrose, ferric oxide, and kieselguhr,parts by Weight of glycerol, 21 parts by Weight of and masticating intothe rubber at a temperature of Water, and 30 parts by Weight of urea; 15about 90 F.,

Ia second sub-mix which itself comprises the said 8 forming a rstsub-mix by heating and mixing to homoparts by Weight of the firstsub-mix together with 10 geneity glycerol, water, urea and ammoniumcarbonparts by weight of methyl violet; 6 parts by Weight ate, coolingsaid tirst sub-mix and mixing with methof a third sub-mix which itselfcomprises 17 parts by yl violet to thereby form a second sub-mix,forming Weight of stearic acid, 80 parts by Weight of glycerol, 20 athird sub-mix by heating and-mixing to homogene- 3 .parts `by weight of10% aqueous ammonia soluity stearic acid, glycerol, aqueous ammoniasolution tion and 12 parts -by weight of water; and 0.2 part and water,cooling said third sub-mix, and forming Iby weight of zinc stearate, 6parts lby Weight of sula fourth sub-mix by mixing together tohomogeneity phur and 1 part by Weight of accelerator, all said zincstearate, sulphur, accelerator, saidV second subhomogeneous mixturesbeing dispersed throughout mix and said third sub-mix, and masticatinginto the rubber at ambient temperature. 12. The method of preparing theself-inking material of claim 3 comprising the steps:

masticating together 17 parts by weight of synthetic Weight of water,1/2 part by weight of potassium hy- 30 polyisoprene rubber and 3 partsby Weight of Ynatural droxide and 11/2 parts by Weight of ferric oxide,rubber,

a second homogeneous mixture of 31/2 parts by Weight grinding and mixingto homogeneity one part by weight of lycerol, 1/2V art b weight ofsucrose, 1/2 art by of water, 0.5 art b wei ht of otassium h droxideWeigght of ferricpoxide 11/2 parts by weight ofpgraphand 1.5 partspbyWseightgof ferlric oxide, asi/1d after it; ml 3 parts by weight ofkieselgushr, andb 35 mixing mastibcating sagre into the rubber at a tem-Y a t ir omogeneous mixture comprising parts y peratureo aout 90 Weightof a iirst sub-mix which itself comprises 22 grinding and mixing tohomogeneity 3 parts Iby weight parts by weight of glycerol, 21 parts byweight of of glycerol, 1/2 part by weight of sucrose, 1/2 part by water,parts by weight of urea and 0.6 part by Weight of ferric oxide, 11/2parts by weight of graphweigh ofbamrnonihun1 carbonate; th .d 8 rt b 40ite and 3 parts lily Weiggklit of kieselguhr, and mastliacata secon su-mix W ic comprlses e sai pa s y mg same into t e ru` er at atemperature of a out Weight of the iirst sub-mix together with 10 parts90 F., by weight of methyl violet; 6 parts by weight of a forming afirst sub-mix by heating and mixing to homothird sub-mix which itselfcomprises 17 parts by geneity 18 parts by Weight of glycerol, 2l partsby weight of stearic acid, 80 parts by Weight of glycerol, 45 weight ofwater, 30 part by weight of urea and 0.6 3 parts by weight of 1,0%aqueous ammonia solution part by weight of ammonium carbonate; cooling 8andV 12 parts by weight of Water; and 0.2 part by parts by Weight ofsaid first sub-mix and mixing with weight of zinc stearate, 6 parts byweight of sulphur l0 parts by Weight of methyl violet to thereby formand 1 part by weight of accelerator, all said homoa second sub-mix;forming a third sub-mix by heatgeneous mixtures being dispersedthroughout the ing and mixing to homogeneity 17 parts by Weight ofrubber. stearic acid, 70 parts by weight of glycerol, 3 parts by 10. Themethod of preparing the self-inking material Weight of 10% aqueousammonia solution and 12 of claim 6 comprising the steps: parts by weightof water; cooling 6 parts by Weight masticating together said syntheticpolyisoprene and of said third sub-mix; and forming a fourth sub-mixnatural rubber, grinding and mixing to homogeneity by mixing together tohomogeneity 0.2 part by weight Y said rst homogeneous mixture containingpotassium of zinc stearate, 6 parts by weightV of sulphur, 1 parthydroxide arid ferrie oxide, and masticating same by weight ofaccelerator, all of said second sub-mix ino the rubber, h and said 6parts h Weilt of said ltahird sub-mix; and

dV ix' to om d t masticatin i tot e rul er at am tt gndloriilagiriiggglllycleril, sucrosii xiceilandnliiieslerl l g n len temperature guhr,and masticating same into the rubber, References Cited forming a thirdhomogeneous mixture by iirstly form- UNITED STATES PATENTS ing a firstsub-mix by-heating and mixing to homo- .n geneity glycerol, Water, ureaand arnmoniurn carbon- 2022887 12/1935 Kf'man 26o-764' ate; cooling saidfirst sub-mix and mixing with meth- 2149211 2/1939 Escher 26o-764 ylviolet to thereby form a second sub-mix; forming 2,267,620 12/1941Cassel 2607-764 a third sub-mix by heating and mixing to homo- 3 19201M1962 Clancy et al lOl-327 geneity stearic acid, glycerol, aqueousammonia solution and water, cooling said third sub-mix; and forming afourth sub-mix by mixing together to homo- MURRAY TILLMAN, PrimaryExaminer. 0 M. J. TULLY, Assistant Examiner,

1. A SELF-INKING MATERIAL COMPRISING RUBBER SELECTED FROM THE GROUPCONSISTING OF NATURAL RUBBER, SYNTHETIC POLYISOPRENE, AND A MIXTURE OFNATURAL RUBBER AND SYNTHETIC POLYISOPRENE, SAID RUBBER CONTAINING: (I)THE FOLLOWING MATRIALS DISPERSED THROUGHOUT THE RUBBER, AN ORGANIC DYE;HYDROSCOPIC SUBSTANCES INCLUDING GLYCEROL PRESENT IN SUFFICIENT AMOUNTTO RETAIN MOISTURE AND PROVIDE AN INK-RETAINING MEDIUM; DISCRETE FILLERMATERIALS INERT WITH RESPECT TO SAID RUBBER, AND A RELEASE AGENT PRESENTIN SUFFICIENT AMOUNT TO PREVENT TACKINESS OF THE MATERIAL, COMPRISING AFATTY ACID MATERIAL OR SALT THEREOF DISPERSED THROUGHOUT THE RUBBER, AND(II) POTASSIUM HYDROXIDE IN SAID RUBBER PRESENT IN SUFFICIENT AMOUNT TOCATALYZE FORMATION OF DYE RETENTION RESIN MOLECULES WITHIN THE RUBBER,THE DYE RETENTION RESIN MOLECULES RELEASING DYE UPON ABSORPTION OFATMOSPHERIC MOISTURE INTO THE RUBBER BY THE HYGROSCOPIC SUBSTANCES.